The effect of turbulence on mass transfer in solid fuel combustion: RANS model

Abstract In this paper, a kinetic-diffusion surface combustion model is examined. The model is modified such that two effects of turbulence are included: 1) enhancement of the mass transfer due to relative velocity between particles and fluid and 2) reduction of the mass transfer due to turbulence-induced particle clustering. Details of the implementation are discussed and the influence of parameters such as air-fuel ratio, particle number density, particle diameter, turbulence intensity and characteristic length scales are studied theoretically. A simplified numerical model of a combustion chamber is created to explore the effects of the combustion model predictions. Finally, the model is incorporated into simulations of an industrial-scale boiler to investigate the effect of turbulence on the net surface reaction rate in a real system. The study shows that although on average this effect is rather minor, there exist regions in which the carbon conversion rate is either decreased or increased by turbulence.